Pre-press color proofing is a procedure that is used by the printing industry for creating representative images of printed material, without the high cost and time that would be required to produce printing plates and set up a high-speed, high-volume, printing press to produce an example single of an intended image. These intended images may require several corrections and may need to be reproduced several times to satisfy or meet the requirements of customers, resulting in a large loss of profits and ultimately higher cost to the final customer.
One such commercially available image processing apparatus, which is depicted in commonly assigned U.S. Pat. No. 5,268,708 is an image processing apparatus having half-tone color proofing capabilities. This image processing apparatus is arranged to form an intended image on a sheet of thermal print media by transferring colorant from a sheet of donor material to the thermal print media by applying a sufficient amount of thermal energy to the donor sheet material to form an intended image. This image processing apparatus is comprised generally of a material supply assembly or carousel, a lathe bed scanning subsystem (which includes a lathe bed scanning frame, a translation drive, a translation stage member, a printhead, and vacuum imaging drum), and thermal print media and donor sheet material exit transports.
The operation of the image processing apparatus as described above comprises metering a length of the thermal print media (in roll form) from the material assembly or carousel. The thermal print media is then measured and cut into sheet form of the required length, transported to the vacuum imaging drum, registered, wrapped around and secured onto the vacuum imaging drum. Next a length of donor material (in roll form) is also metered out of the material supply assembly or carousel, measured and cut into sheet form of the required length. It is then transported to and wrapped around the vacuum imaging drum, such that it is superposed in the desired registration with respect to the thermal print media (which has already been secured to the vacuum imaging drum).
After the donor sheet material is secured to the periphery of the vacuum imaging drum, the scanning subsystem or write engine provides the scanning function. This is accomplished by retaining the thermal print media and the donor sheet material on the spinning vacuum imaging drum while it is rotated past the print head that will expose the thermal print media. The translation drive then traverses the print head and translation stage member axially along the vacuum imaging drum, in coordinated motion with the rotating vacuum imaging drum. These movements combine to produce the intended image on the thermal print media.
After the intended image has been written on the thermal print media, the donor sheet material is then removed from the vacuum imaging drum. This is done without disturbing the thermal print media that is beneath it. The donor sheet material is then transported out of the image processing apparatus by the donor sheet material exit transport. Additional donor sheet materials are sequentially superimposed with the thermal print media on the vacuum imaging drum, then imaged onto the thermal print media as previously mentioned, until the intended image is completed. The completed image on the thermal print media is then unloaded from the vacuum imaging drum and transported to an external holding tray on the image processing apparatus by the receiver sheet material exit transport.
Although the presently known and utilized image processing apparatus is satisfactory, it is not without drawbacks. In an image processing apparatus, as the imaging drum spins, the printhead moves along the vacuum imaging drum in a path that is parallel to the longitudinal axis of the vacuum imaging drum (referred to as the slow scan). The translation drive moves the printhead in the "slow scan" direction, from a home position (at the point where it begins writing the intended image using the data from the image processing apparatus) to the opposite end of the vacuum imaging drum. The combined movement of the printhead and the vacuum imaging drum rotation perpendicular to the motion of the printhead causes the resulting image to be written in a single, continuous helix about the vacuum imaging drum. However, with the present image processing apparatus, at the end of a writing cycle the printhead must be returned to the home position before writing the next color in order to assure, for example, color to color registration. Returning the printhead to the home position prior to unloading and loading of media and for the start of the next image scan adversely affects the throughput of the image processing apparatus.